Various infections (particularly acute childhood exanthematous diseases) and vaccinations can be accompanied or followed by several types of encephalomyelitis:

• acute disseminated encephalomyelitis (ADE)
• parainfectious encephalomyelitis
• postinfectious encephalomyelitis (PIE)
• postvaccinal encephalomyelitis (PVE)

Clinical symptoms and pathologic changes are similar regardless of the precipitating infection or vaccination.96

Common infectious states that can be accompanied or followed by signs and symptoms of an encephalomyelitis include:

• measles
• rubella
• varicella
• mumps
• influenza
• parainfluenza
• cytomegalovirus (CMV) infection
• mycoplasmal infection
• upper respiratory infection

Vaccinations that can precipitate PVE include:

• measles
• mumps
• rubella
• influenza
• rabies

CNS reactions can also occur after inoculations with sera, particularly against tetanus.96,193

CNS damage after acute exanthematous infection occurs most commonly following measles, for which the incidence is approximately 1 per 1,000 cases.193 In regions with high vaccination rates, however, measles is no longer a common cause of PIE. (The incidence of PVE following measles vaccination is only about 1 per 1 million recipients).193 Varicella is now probably the most common specific etiology of PIE, although the exact incidence is unknown. Nonspecific upper respiratory infections are probably the most common cause overall.96,193

The pathogenesis of ADE, PIE, and PVE is unknown. An allergic or autoimmune reaction is most likely. Presumably a pathogen, usually a virus, triggers an immune-mediated reaction against CNS myelin, causing a disease similar to experimental allergic encephalomyelitis.193

The characteristic pathologic change is demyelination.96,193 Lesions are usually numerous and diffusely distributed. Although concentrated in white matter, a few patches can be found in cortical gray matter, with consequent epileptogenic potential. Acute hemorrhagic leukoencephalomyelitis appears to be a fulminant form of ADE, PIE, and PVE. Its pathology is similar to ADE, PIE, and PVE, with the addition of microscopic hemorrhages and perivascular neutrophilic infiltrates.96,193

The clinical manifestations of AED, PIE, and PVE correspond to the CNS component most damaged. Syndromes involving the spinal cord, meninges, basal ganglia, cerebellum, and cortex are well described. Meningitic signs (e.g., headaches, nuchal rigidity) are common early in the course of all types of ADE, PIE, and PVE.96 Acute toxic encephalopathy and Reye’s syndrome are seen more frequently after varicella, influenza, and rubella. In encephalitic forms, focal and generalized seizures can occur and can constitute the initial presentation.194–198

Diagnosis

Because there is no specific diagnostic test, ADE, PIE, and PVE should be considered when neurologic signs develop within 1 month of the onset of acute exanthemata, upper respiratory tract infection, or vaccination. The differential diagnosis includes practically all acute infectious and inflammatory diseases of the CNS, including acute diffuse multiple sclerosis.96,197,198

Lumbar puncture yields the following CSF profile:

• opening pressure: can be slightly elevated
• protein: normal or slightly elevated
• glucose: normal
• moderate pleocytosis (lymphocytic)
• myelin basic protein: usually increased

EEG is abnormal in most cases, usually with slow frequency (4–6 Hz) and high voltage.96 Abnormalities are usually generalized and symmetric, but focal and unilateral changes can be found that can persist for weeks after apparent clinical recovery.96 Persistent EEG abnormalities correlate with persistent neurologic abnormalities, including residual epilepsy.96

MRI can reveal assorted white-matter lesions.196–198

Treatment

There is no definitive treatment. Steroids can ameliorate the symptoms. Maintenance anticonvulsant treatment, according to routine guidelines, often is required.194

Adapted from: Goldstein MA and Harden CL. Infectious states. In: Ettinger AB and Devinsky O, eds. Managing epilepsy and co-existing disorders. Boston: Butterworth-Heinemann; 2002;83-133.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised March 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.

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